CVE-2017-7840 in Firefox
Summary
by MITRE
JavaScript can be injected into an exported bookmarks file by placing JavaScript code into user-supplied tags in saved bookmarks. If the resulting exported HTML file is later opened in a browser this JavaScript will be executed. This could be used in social engineering and self-cross-site-scripting (self-XSS) attacks if users were convinced to add malicious tags to bookmarks, export them, and then open the resulting file. This vulnerability affects Firefox < 57.
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Analysis
by VulDB Data Team • 03/22/2023
This vulnerability represents a sophisticated cross-site scripting flaw that exploits the bookmark export functionality within the Firefox browser. The security issue stems from insufficient input validation and sanitization of user-supplied data during the bookmark export process. When users create bookmarks with malicious JavaScript code embedded within tags or labels, the export mechanism fails to properly escape or filter this content, allowing the malicious code to persist in the resulting HTML file. The vulnerability specifically affects Firefox versions prior to 57, indicating a long-standing issue that was addressed through subsequent security updates. This type of vulnerability falls under the CWE-79 category for Cross-Site Scripting, where the flaw occurs in the output generation phase rather than input processing, making it particularly dangerous due to its indirect execution path.
The operational impact of this vulnerability extends beyond simple script execution to encompass sophisticated social engineering attack vectors. An attacker could craft malicious bookmark entries containing JavaScript code that would execute when the exported HTML file is opened in a browser, creating a self-XSS scenario where users inadvertently execute malicious code through seemingly legitimate bookmark management activities. The attack requires user interaction to complete the malicious workflow, as victims must first add malicious tags to bookmarks, export them, and then open the resulting file. This dependency on user action makes the vulnerability more challenging to exploit at scale but still poses significant risk in targeted attacks where social engineering can be effectively employed. The attack surface is limited to users who regularly export bookmarks and open the resulting HTML files, but this encompasses a substantial portion of Firefox users who manage their browser bookmarks extensively.
The technical exploitation of this vulnerability demonstrates the importance of proper content sanitization in web applications and browser environments. When Firefox processes bookmark data for export, it fails to implement adequate security measures to prevent JavaScript code injection into the generated HTML output. This oversight creates a persistent security risk where legitimate browser functionality becomes a vector for malicious code execution. The vulnerability is particularly concerning because it leverages trusted browser features to deliver malicious payloads, making detection more difficult for users and security tools. From an ATT&CK framework perspective, this vulnerability maps to techniques involving social engineering and user execution, where the attack chain relies on user trust and the perceived legitimacy of bookmark management functions. The exploitation pattern aligns with tactics that involve initial access through user interaction, followed by code execution within the browser context, making it a valuable vector for attackers seeking to establish persistent access or deliver additional payloads.
The mitigation strategy for this vulnerability involves immediate browser updates to version 57 or later, where Mozilla implemented proper input sanitization and output encoding for exported bookmark data. Users should also exercise caution when opening exported bookmark files from untrusted sources and implement additional security measures such as browser security extensions that can detect and block potentially malicious content. Organizations should ensure their Firefox installations are maintained at current security levels and consider implementing security policies that restrict bookmark export functionality in high-security environments. The vulnerability serves as a reminder of the critical importance of input validation and output encoding in web applications, particularly when dealing with user-generated content that will be rendered in browser contexts. Regular security audits of browser functionality and export features can help identify similar vulnerabilities before they can be exploited by malicious actors.